The IEEE 802.16 standard specifies a fixed and mobile Broadband Wireless Access (BWA) standard for a wireless Metropolitan Area Network (MAN). The IEEE 802.16 standard defines different physical layer technologies for different frequency bands.
In current communication systems, multicast and broadcast techniques are employed for transmitting data from one source to multiple destinations. In order to effectively utilize radio resources, the IEEE 802.16e standard has introduced the Multicast and Broadcast Service (MBS) that standardizes the point to multi-point transmission in the mobile network. The MBS service may support not only the multicast and broadcast of low bit-rate message services such as text, but also the multicast and broadcast of high bit-rate multimedia services. Below is a citation from an IEEE 802.16e standard (Section 6.3.23 Multicast and broadcast services in ‘IEEE Std 802.16e™-2005 and IEEE Std 802.16™-2004/Cor1-2005′) with regard to the MBS: “Some globally defined service flows may carry broadcast or multicast information that should be delivered to a plurality of SS or MS. Such service flows have certain QoS parameters and may require encryption performed using a globally defined sequence of TEKs. Since a multicast or broadcast transport connection is associated with a service flow, it is associated with the QoS and traffic parameters for that service flow. Some MS are registered to certain BS while some are in Idle mode and not currently served by any specific BS. Two types of access to multicast and broadcast services (MBS) may be supported: single-BS access and multi-BS access. Single-BS access is implemented over multicast and broadcast transport connections within one BS, while multi-BS access is implemented by transmitting data from Service Flow(s) over multiple BS. MS may support both Single-BS and Multi-BS access. ARQ is not applicable to either single-BS-MBS or multi-BS-MBS. Initiation of MBS with respect to specific MS is always performed in registered state by creation of multicast connection carrying MBS data. During such initiation the MS learns the Service Flow ID that identifies the service. For multi-BS-MBS, each BS capable of providing MBS belongs to a certain MBS Zone, which is a set of BSs where the same CID and same SA is used for transmitting content of certain Service Flow(s). MBS Zone is identified by a unique MBS_ZONE identifier”. It should be understood that more details about MBS can be found in the standard.
A Subscriber Station (SS) receives the MBS service through the indication in the MBS_MAP message. The MBS_MAP message provides information on physical channel resources allocated for a specific Multicast Connection Identifier (CID), i.e. an MBS service, in a given MBS ZONE. According to the 802.16 standard, the CID is defined as a 16-bit value that identifies a transport connection or an uplink/downlink pair of associated management connections to equivalent peers in the MAC of the BS and SS. The physical channel resources include occupied OFDM symbols and used Sub-channels. The MBS_MAP message also provides Downlink Interval Usage Code (DIUC), which is an interval usage code including the information of modulation and coding scheme for identifying a particular burst profile used by a downlink transmission interval, and Boosting for a given burst, and the Next MBS frame offset and the Next MBS OFDMA Symbol offset for determining the location of the next MBS frame. When receiving an MBS frame, the SS locates the MBS_MAP message according to an MBS_MAP Information Element (MBS_MAP_IE) in a Downlink (DL_MAP) message, and then the SS can determine the physical channel resources and DIUC parameter for this service. So the SS is capable to know the start transmission point, occupied subchannel(s) and occupied OFDMA symbol(s) inside the MBS ZONE.
FIG. 1 is a signal diagram illustrating a connection creation procedure for an MBS service of the prior art. The CID allocation 100 includes: an SS transmits a DSA_REQ (Dynamic Service Addition Request) message to the BS to set up an MBS connection in step 101; in step 102, the BS transmits to the SS a DSX_RVD (Dynamic Service X Received) message, which is normally used to inform the SS that the BS receives a DSA-related message such as the DSA_REQ message and will handle the received message; in the step 103, the BS transmits a DSA_RSP (Dynamic Service Addition Response) message that contains the information responsive to the DSA_REQ message; upon receiving the DSA_RSP message, in the step 104, the SS transmits a DSA_ACK (Dynamic Service Addition Acknowledge) message. In the course of one connection creation procedure, a Connection Identifier (CID) that uniquely identifies the MBS service connection is allocated.
Efficient and reliable delivery of video data is becoming increasingly important especially in wireless communication environment. Layered coding is a family of data representation techniques where the source data is partitioned into multiple layers. The layers are organized normally in a way that the lowest layer also called as base layer contains the minimum information for intelligibility; the other layers also called as enhancement layers contain additional information that incrementally improves the overall quality of the source data. When the layered coding technique is applied into video codec, the video data is normally encoded into multiple layers including a base layer of comparatively low quality video and at least one enhancement layer of increasingly higher quality video. On the receiver side in a layered coding communication system, a decoder can be configured to choose and decode a particular subset of these layers to get a particular quality of the video according to its preference and decoding capability.
FIG. 2 is a diagram schematically illustrating an example of downlink frame structure of the prior art. As shown in the FIG. 2, the preamble region 201 is used for transmitting a synchronization signal, i.e., a preamble sequence, for acquiring mutual synchronization between a BS and an SS. The DL_MAP region 203 is used for transmitting a DL_MAP message, and includes an MBS_MAP information Element (MBS_MAP_IE) region when MBS is provided. The MBS_MAP_IE region includes information necessary for decoding an MBS field that is comprised of MBS_MAP region 205 and fields 207 to 217. The MBS_MAP region 205 is used for transmitting a MBS_MAP message that includes location information where an SS receiving an MBS service receives MBS data bursts, and information necessary for decoding the data bursts. Contents of fields 207 to 217 are conveyed on data bursts. In this example, two MBS services of each containing three layers are presented, i.e. MBS services of session 1 and session 2, and each MBS service is provided with a base layer and two enhancement layers. When an SS receives an MBS service, the SS will decode at least one layer according to its decoding capability and preference.
However, there are some drawbacks. Assuming an SS intends to watch the MBS service of Session 1 and it has capability to decode all layers associated with the Session 1, thus, in order to receive all the data, the SS needs to perform 3 times the CID allocation procedure 100 in order to obtain CIDs for layers of SESSION1_BASE, SESSION1_ENHANCEMENT1, and SESSION1_ENHANCEMENT2. Thus, it is desirable to reduce the number of message exchange when obtaining CIDs of all layers for an MBS service.